96 Grand Voyager noise at 15000 rpm

[phreakb0y]

I just overhauled my 3.3L engine and replaced all the gaskets and the serpentine belt. The engine is strong and runs very quiet with the exception of when I'm driving. At 1500 rpm it makes a vibration noise in the engine compartment near the serpentine belt area. It doesn't make that sound when it's in park, only when in drive. Also it doesn't make a sound at rpms higher or lower than 1500. My brother who used to be a mechanic for Chrysler says it sounds like it might be the tensioner pulley, however, he can't know for sure unless he looked at, which makes it hard since he lives 2500 miles away. I turned off the heater to rule out the AC and it still made the noise. Any appreciation would be helpful.

Dan